Here are the possible solutions for they don't last clue
Answer
Clue
Relevancy
ephemera
Clue
They don't last
Definition
(Greek) an insect of the mayfly genus Ephemera, whose adult life is very short
fads
Clue
They don't last long
They don't last
Definition
FAD, a hobby or interest that enjoys brief popularity
seanbean
Clue
Actor whose first and last names look like they rhyme, but don't
rockbottom
Clue
With 133, the name of the band whose members appear in the theme answers. (They disbanded in 2012 after raising millions for literacy, but they're reuniting this weekend for one last concert.)
